The present invention relates to an electrolyte reservoir for use in molten carbonate fuel cells and to methods of preparing such a structure.
Generally, molten carbonate fuel cells are comprised of a cathode, an anode, and an electrolyte structure disposed between the cathode and the anode. The electrolyte structure is composed of carbonate electrolyte in a supporting matrix. Under fuel cell operating conditions, at temperatures usually in the range of about 500.degree. C. to about 700.degree. C., the supporting matrix acts to retain, via capillary action, the electrically active molten carbonate between the cell electrodes, thereby alleviating the need to physically anchor the electrodes as rigidly as would be required with a pure electrolyte system.
One of the principal problems facing the development of carbonate fuel cells is how and where to store sufficient electrolyte to maintain adequate performance over the cell life which may be 40,000 to 50,000 hours. During cell operation electrolyte is lost by several processes, such as vapor transport or reaction with cell components. One state of the art cell design employs the use of a thick tile between the anode and the cathode in which to store sufficient electrolyte to maintain required performance during the cell life. However, cells with such thick tiles suffer from high IR losses. Another concept currently being evaluated is the use of a relatively thin matrix for the electrolyte between the anode and the cathode with the required excess electrolyte being stored in the electrodes. This concept results in flooding the electrode with electrolyte which increased the internal resistance of the cell and degrades performance. Another problem with both concepts is that as electrolyte is lost from the matrix, porosity of the matrix develops which itself contributes to increased cell resistance and if the porosity becomes interconnected, anode and cathode gases can mix, which seriously reduces cell performance. An additional problem is that as the matrix becomes more porous the structure is weakened and can crack, again leading to cross leaks.